Ballast unit for gas discharge lamps

ABSTRACT

A ballast unit system for various types of gas discharge lamps, in particular for fluorescent tubes, mercury and sodium vapor lamps, comprising a ballast choke. The lamp circuit is arranged in parallel with at least one semiconductor switching means or a triggering means which are designed to operate at the magnetic saturation bend for the purpose of developing the firing voltage required for lamp starting. In cases where heated lamps are used the switching or triggering means are designed for brief preheating of the lamps with increased rated current. The starter has no mechanical or moving parts, thereby minimizing wear and maximizing dependability.

United States Patent 1191 Vogeli Dec. 2, 1975 1 BALLAST UNIT FOR GASDISCHARGE LAMPS [76] Inventor: Ernest Jakob Vogeli,

Friesenbergstrasse 40, 8055 Zurich,

Switzerland [22] Filed: May 24, 1972 [21] Appl. No.: 256,452

[30] Foreign Application Priority Data May 24, 1971 Austria 4476/71 May16, 1972 Switzerland 7220/72 [52] US. Cl. 315/97; 315/101; 315/103;315/105; 3l5/DlG. 5

[51] Int. Cl. H05B 41/14 [58] Field of Search..... 315/D1G. 2, DIG. 5,DIG. 7, 315/94-101, 103, 105

Vogeli 315/010. 5 Kaneda et al v. 315/1310. 5

Primary Examiner-John K. Corbin Assistant ExaminerRichard A. RosenbergerAttorney, Agent, or Firm-Browdy and Neimark [57] ABSTRACT [56]References Cited or moving parts, thereby minimizing wear and maxi-UNITED STATES PATENTS "filing dependability 3,519,881 7/1970 Engel et a1315/1310. 5 21 Claims, 13 Drawing Figures |r T 1 103 Il-X US. PatentDec. 2, 1975 Sheet 1 of6 3,92,155

US. Patent Dec. 2, 1975 Sheet 2 of6 3,924,155

US. Patent Dec. 2, 1975 Sheet 3 of6 $924,155

0 H T 1 103 IZPv- 108 12l== FIG,6

FIG.8

Patent Dec. 2, 1975 Sheet 5 of 6 3,924,155

US, Patent D66. 2, 1975 Sheet 6 of6 3,924,155

Fig. 13

BALLAST UNIT FOR GAS DISCHARGE LAMPS The present invention concerns aballast unit for gas discharge lamps, in particular for fluorescenttubes, mercury and sodium vapor lamps, comprising a ballast choke.

The Swiss Pat. No. 431.716, 431.717 and 446.524 have disclosedquick-heating ballast units which, however, have not been approved fortrade or installation because, on a fault arising, i.e., when the tubeis deactivated or the gas fill is disturbed, the system has noquick-acting cut-off protection against the continually overdosedcurrent and is therefore liable to bum-out, i.e., destruction of tubeand choke. Nor do those circuits provide for wattless currentcompensation or gradual increase of the firing current to prevent coldstarting. The German Pat. Nos. 837.419 and 949.419 have disclosedcircuits which, however, have neither any feedback quick-heatin gsystems nor any protection against early firing and which therefore havesimilar disadvantages as have the starterless systems.

The object of the present invention is to provide ballast unit systemsfor the various types of gas discharge lamp which are technologicallybetter and/or less expensive than known systems. In particular a. thestarter part is not to have any mechanical or moving parts and is thusto minimize wear and maximize dependability;

b. the system is not to have any additional transformers, iron cores andcoils other than the copper and iron core required for the choke, inorder not to increase weight, size and copper/iron losses needlessly;

c. the system is to use an increased preheating current higher than therated current of the lamp in order to ensure pleasant, flicker-freestarting of the preheated lamp;

d. cut-off of the preheating is not to depend on static conditions, suchas a favorable ambient temperature which may trigger a cold start, butinstead a certain minimum safety quantity of preheating energy is toensure the filament flow temperature in any conditions;

e. the system is to rule out any overheating or bumout of the system inthe event of a fault arising, i.e. in the event of de-activatedfilaments, disturbed gas fill, etc.;

f. the firing voltages are to be higher than the mains voltage to theextent that, at a normal ambient temperature, no special lamps (such astubes with ignition strips) are required.

The systems disclosed by the patents cited each only fill the aboverequirements in part, in particular:

Swiss Pat. No. 431.716 fails to meet points (b), (d),

Swiss Pat. No. 431.717 fails to meet points (b), (c);

Swiss Pat. No. 446.524 fails to meet points (b), (e);

German Pat. No. 837.419 fails to meet points (c),

German Pat. No. 949.419 fails to meet points 0);

French Pat. No. 582.392 fails to meet points (d), (e).

The present invention provides for a ballast unit which fills all therequirements together. It achieves its object in that there is connectedin parallel to the lamp circuit at least one semiconductor switchingmeans or a triggering means operating at the magnetic saturation bendfor developing the firing voltage required to start the lamp, whichmeans is designed for increased rated 2 current for brief preheating inthe case of heated lamps being used.

While in known circuits it is usually the short-circuit current of thechoke or a separate heating transformer which preheats the filaments ofthe lamp in starting, in the system claimed hereunder the seriesimpedance merely serves current-limiting of the tube firing voltage. Thehigh a.c. impedance of the choke, which is also in the preheatingcircuit, is at all times fully effective on the tube discharge path andis subsequently compensated again by suitable means. Its compensationleaves a sufficiently small residual internal resistance for the purposeof increasing the filament heat-up rate by the much heavier current tothe level desired. This much heavier preheating current, which passesthrough the filaments and the series inductance, but never through thedischarge path, would be far too high to be sustained as an effectivecurrent by the choke winding and the filaments. It only keeps within thetime-safe limits owing to its being a current surge which is exactlytime-dosed and controlled and monitored by the lamp itself. Itsmagnitude is only little below the zone in which an emission-damagingcross-firing across the filament could arise. This dangerous zone beginsat about 15 20 times the rated current heating power, depending on thetype of lamp. The result is a quickstarting, flicker-free ballast unitwhose switch-on time approximately corresponds to that of anincandescent bulb.

Several embodiments of the invention are now to be described by way ofexample with reference to the drawings, in which FIGS. 1 11 show circuitdiagrams of several embodiments;

FIG. 12 shows the trend of the tube voltage for various switching phasesof the ballast unit;

FIG. 13 (a-i) shows the trend of the tube voltage for the variousembodiments.

The embodiments shown in. FIGS. 1 5 comprise a choke which is connectedto the mains terminals 1 and 2 and which consists of two windingsections 3a and 3b wound on to a common core 4. In asymmetrical chokes,the series inductance would consist of a single winding. Such a seriesinductance can also be formed by a stray field transformer. The gasdischarge lamp 6 is connected on one side by its two filaments 5 and 7to the choke sections 3a and 3b. The other two filaments 8 and 9, whichin known ballast units are carried to a bimetal glow starter, are passedto the electronic starting and firing assembly. In all circuit examplesshown, a thyristor or a triac (a.c. thyristor) performs the function ofthe starting switch.

In FIG. 1, compensation of the series inductance 3a and 3b is effectedby an additional winding 10, 11 which is wound onto the same iron core 4as is the choke. Its winding direction is opposite to that of the choke,but the number of windings is the same. Once the unit is connected tothe mains terminals 1 and 2 and the triac 12 is fully activated(conductive), there arises an approximately induction-freelow-resistance heating circuit 1, 3a, 5, 8, 10, 12, 9, 7, 3b, 2 whichresults in a very rapid heat-up of the filaments 5 and 7. The far moreresistive a.c. circuit 1, 3a, 5, 6, 7, 3b, 2 across the discharge pathremains fully preserved and performs the function of limiting the firingcurrent. The rectifier bridge 15 18, which at first has no d.c.potential owing to the capacitor 13, begins to charge, and the voltagedrop across the voltage-dependent resistor 19,

which works as a load resistor, becomes continually smaller. The controlvoltage for the trigger diode 23 passed by the series resistor 21 to thetrigger capacitor 22 becomes continually smaller. The firing points inthe triac now no longer arise shortly after the zero passage of the mainsinusoidal voltage curve (FIG. 12), but shift towards the apex. However,at the firing moment, the triac 12 not only closes the heating circuit,but also connects the mains voltage capacitor 25 to the primary 11 of anautotransformer l0, 11, so that a high-voltage firing peak arises in thesecondary 10, causing firing of the lamp. The size of the capacitor 25is such that it also converts the ballast unit, otherwise inductive,into a wattless-current-compensated unit. The third function of thecapacitor 25 is to permit the copper crosssection of the ballast windingto be approximately halved owing to the wattless current gain in thechoke. Its fourth function is to cut off any overvoltage peaks which mayarise in the mains and damage the triac. The assembly further comprisesa safety discharge resistor 26 and a safety diversion resistor 24.

Once the triac fires, the voltage across the tube is approximatelyhalved (FIG. 12b), because all the windings practically operate in shortcircuit and act on an ohmic voltage divider. A radio interferencesuppressor 29 does not affect the starting and firing functions. Theelectronic control assembly 13-24 for the triac 12 serves threedifferent control states, in particular:

1. The switch-on phase:

Immediately after switch-on, the timeand voltagedependent voltagedivider arrangement 13 22 controls the trigger diode and, accordingly,the triac in such a manner that the latter remains fully switched on.The tube 6 receives a high heating current, but no firing voltage, andabout half the mains voltage.

2. The starting phase:

While the filament temperatures rapidly approach the glow level, thecapacitor 13 charges and, through the delayed triac firing, the fullmains voltage occasionally reaches the tube across the choke. Owing tothe shortened triac switching time, the heating current becomes slightlysmaller, and the firing peaks become greater from one halfwave to thenext. At the moment when firing begins, the voltage across the tubecollapses, and the capacitor 13, now overcharged, causes completecut-off of the triac 12. The size of the delay capacitor 13 is such thatreadily heatable lamps are ready for firing towards the end of theswitch-on phase. For other lamps, the rapid heating continues asnecessary.

3. The protection phase:

If, despite the starting phase being prolonged about fivefold, the tubehas still not fired, the capacitor 13 will keep charging because of thepersistent firing peaks until there is no longer any triggerable voltageacross the capacitor 22. The discharge resistor 14 slowly reduces thecharging voltage until isolated firing and heating pulses again becomepossible (FIG. 12d). The time element 13, 14 begins to swing up and downat the rate of once or twice a second. The resistor 14 can be soadjusted that the tube rated current arises as the effective value,which, even when sustained, cannot burn out the winding and whichpermits the tube to start after removal of the fault (e.g., too low amains voltage). Moreover, the resistor 14 in conjunction with thecapacitor 13 corresponds to a time element with the same time constantas the cool-down rate of the tube filaments, so that, after a shortfiring pause, the

Resistor l4 about 470 kilohms Capacitor l3 about 1 uF Resistor 2i aboutl5 kilohms Capacitor 22 about 47 nF Resistor 24 about 1 kilohmsCapacitor 26 about 4 p.F Resistor 26 about 100 kilohms Capacitor 29about 10 nF Resistor 28 about O...47 kilohms Number of windings (seriesinductance 100%) 3a about 50% 3b about 50% 10 about 90% l I about 10%FIG. 2 shows a second embodiment which'partly compensates the highseries impedance 3a and 3b, which hinders accelerated flicker-freefilament heatup, yet without reducing such impedance for the purposes oflamp current limiting. This function is performed by a capacitor 30,which acts in opposition to the series inductance. The apparentresistance of the capacitor 30 must be about 2 3 times smaller than thatof the series inductance in order to avoid any resonance effect and tokeep the initial voltage across the tube as low as possible.

In FIG. 2, the capacitor 30 is in series with a triac 31, which, afterthe beginning of switch-on, is controlled for full conductivity, becausethe harmonics-eliminating voltage divider 38-41 almost continually actson the trigger diode 43 across the bridge rectifier 34-37, which is atfirst still short-circuited. The collapse of the tube voltage to thefiring voltage renders the triac control ineffective. The R-C element45, 46 constitutes a radio interference suppressor. As in starterlesssystems, the circuit has no firing voltage and, besides ensuring a muchquicker start, it provides better early firing protection due to thereduced initial voltage.

For example, the values of the switching elements for v the circuit maybe:

Resistor 33 about Resistor 38 about 3.3 megohms 22 kilohms Capacitor 32about I [.l-F Capacitor 39 about 47 nF FIGS. 3, 4 and 5 show embodimentsin which an unequally heavy one-sided halfwave load in the choke resultsin a high d.c. component and therefore in the heating current increasedesired. The circuits shown in FIGS. 3 and 4 also include means designedto rule out early firing especially in short tubes, i.e., tubesespecially liable to cold starting.

FIG. 3 shows a circuit in which, apart from the suppressor R-C element57, 58, a triac 63 is connected in series with a diode 62 across thestarter connection points 8 and 9. Also, there is a voltage-limitingvoltagedependent resistor 59 across the diode and there is a damping R-Celement 60, 61 across the triac 63, so that, with the triac 63 fullyactivated, a mains voltage approximately halved by the voltage-dependentresistor arises in the one group of halfwaves across the starterconnection points, while a mains voltage shortcircuited by the diode 62arises in the other half-waves (FIG. 130). As the diode 67 has to chargethe time element 64, 65 across the series resistor 66, but is itselfbridged by an opposed diode 68 with a time element 69, 70, the triaccontrol signals diminish in their sequence in such a manner that, withan approximately halved mains voltage across the tube, a highasymmetrical d.c. at first effects preheating. Then, owing to thecontrol shift, the halfwave group passing directly through the diode 62is interrupted, but not so the halfwave group passing through thevoltage-dependent resistor. As a result, a heavy heating currentcontinues to flow, yet at the full mains voltage and at an additionalovervoltage oscillation which is rendered firing-aiding by thesuppressor element 57, 58 (FIG. 13d). When the tube fires, the controlvoltage collapses to about /3 and is no longer capable of beingactivated.

The circuit shown in FIG. 4 is suitable especially for capacitive(wattless-current-overcompensated) ballast units (series capacitor 75indicated by broken line). A triac 63 arranged directly across the lampfiring path 8,9 is controlled across the trigger system 71-74 through aseries resistor 77 and then through two diode time elements 78, 79, 80and 81, 82, 83 which are connected in parallel and are unequallydimensioned and whose diodes have opposed directions. A voltagedependentresistor 76 across the tube discharge path prevents, in the presence ofa capacitor 75, any voltage straying in the more weakly controlledhalfwaves. The delay capacitors 79 and 82, which are at first stilldis-. charged, develop a lamp voltage according to FIG. 7e at the almostfully conductive triac. The weaker, fastercharging time element drivesthe choke into saturation and develops a heavy heating heating current.If the tube did not fire, or fired late, the voltage curve shown in FIG.13g would arise towards the end of the starting process.

FIG. 5 shows a much simplified variant for asymmetrical heating. It issuitable for long lamp types. The dc. saturation already arises from thefact that only a thyristor 84 acts as switch, so that the negativehalfwaves are in any case invariably blocked. A resistor 85 carries acontinual control voltage to the thyristor firing electrode. Afterswitch-on, however, a diode 86 begins to charge the capacitor 88 acrossa seies resistor 87. The increasing negative voltage across thiscapacitor increasingly draws the voltage supplied from the resistor 85into a negative zone, across the resistor 89. When the tube fires, itsfeed voltage collapses. Owing to the negative superimposition, thecontrol current is no longer sufficient for further firings in thethyristor. If the tube fires later or not at all, the increasingnegative influence will eventually cut off the heating. As the RC valuesare such that the filaments glow before the charge of the capacitor 88has reached its maximum, the self-regulating effect is sufficientlygreat to dispense with a trigger diode.

The embodiments shown in FIGS. 6 11 have a choke with an inductancewhich is 2 3 times smaller than that in known units. While a capacitorarranged in the firing circuit in parallel with the inductance isoperated by the mains frequency, the inductance preferably operates onthe third harmonic of the mains frequency. As the current or voltagetrend of the fired tubes is almost square, an almost ideal wattlesscurrent compensation arises when the phase relations are considered. Asthe series inductance is 2 3 times lower than that in known units, thefiring voltage at the lamps is higher,

6 permitting two lamps to be connected in series, each of which formerlyrequired a ballast unit of its own. Thus, the reduced inductance and thepossibility of operating two tubes in series with a single ballast unitoffer substantial savings.

The ballast unit shown in FIG. 6, which is fully operative even withoutthe control circuit indicated in the right section, comprises a seriescapacitor 103, a series inductance 104, which may have the form of anair gap choke, for instance, and further comprises two seriesconnectedtubes a and 105b. The outer filaments of the series-connected tubes areconnected in series with the inner filaments across saturation chokes106a and 106b. Instead, of course, there may be only one saturationchoke 106. The arrangement also includes an interference suppressor 121.To protect the ballast unit from overload, the circuit of the saturationchoke is provided with positive temperature coefficient resistors 107aand 107b, while the main circuit includes a thermal switch 108 bridgedby a resistor.

The saturation chokes 106a and 106b are so dimensioned that, because oftheir steeply rising reactance, they at first only present a very lowresistance to the heating current. When the tubes are fired, however,only a negligibly small current flows through the chokes.

To improve the firing properties of the arrangement shown in FIG. 6, athyristor 112 connected in parallel with the chokes takes over anadditional current quota in one halfwave and is controlled in asubsequent halfwave under the influence of a previously chargedcapacitor 116. The charging of the capacitor 116 is effected across adiode 109 and a resistor 111. The resistors 110 and 113 ensurecorresponding voltage potentials at the control electrode of thethyristor 112. The limiting diodes 114 and 115, which are controlledacross the resistors 118 and 120 and across a diode 1 19 under theinfluence of a capacitor 117, act as overload protection for thethyristor 112.

For a 50 0/5 mains, the values of the switching components used may beas follows:

103 4 F l 16 47 nF 104 Z 300 ohms I17 330 p.F

110 l megohm 1 l8 l0 kilohms I11 150 kilohms 120 l kilohm 113 330kilohms The embodiment shown in FIG. 7 has an electronic firing systeminstead of the two saturation chokes. The inner filaments of theseries-connected tubes 105a and 105k are connected across an auxiliarywinding 136 arranged on the inductance 104.. Owing to the heavy currentwhich also flows in this unit at first, the winding 136 develops arelatively high heating voltage for the inner filaments.

The electronic control circuit developing the increased heating currentrequired to fire the tubes 105a and 105b comprises a triac 122, aresistor 131 and a trigger diode 129. A time element 125, 126 arrangedin a rectifier circuit 127, 128 is connected across a resistanceassembly 123, 124, a capacitor 132 and a further capacitor 130. Infunction, this control circuit largely corresponds to the embodimentsshown in FIGS. 1 3. An assembly comprising a resistor 133, a capacitorand a parallel-connected voltage-dependent resistor 134 providesovervoltage protection for the triac.

A preferred embodiment presents the following values:

123 68 kilohms 126 1 #F 124 l megohm 130 68 nF 125 2.2 megohms 132 150nF 131 l kilohm 135 100 nF 133 33 kilohms The embodiment shown in FIG. 8corresponds in essentials to that shown in FIG. 7, with the differencethat the cold-starting protection for heated tubes is improved.Moreover, the automatic starting system is bridged by an additionalcircuit preventing repeated starting in the event of a fault. Athyristor 144 used as a switch is connected to a capacitor 141 whichserves as cold-starting protection and which is connected across aparallel-connected diode 142 to a measuring resistor 151, particularlyat the gas discharge path. In cold tubes, no voltage is thereforedeveloped. However, once the thyristor 144 has been cut off by anegative voltage drop at the measuring resistor 151 across components145, 146, 147, 148, 152 and 153, the lamps can fire, and the voltageacross the inductance 104, reduced across a resistor 154 and rectifiedby a diode 155, is used to maintain this cut-off. In the event of afault, after several unsuccessful starting att mpts, this function istaken over by a safety cut-off, comprising the components 137, 138, 143,149 and 150. A preferred embodiment presents the following values:

137 47 kilohms 139 nF 140 l megohm 141 64 p.F 151 10 megohms 150 2000 F149 3.3 kilohms 152 680 11F 153 2.2 kilohms 154 47 kilohms Theembodiment shown in FIG. 9 presents a simplification on the versionshown in FIG. 8, in that the additional cut-off means is dispensed with.Also, the automatic trigger and cut-off assembly is simplified in thatthe harmonic quota contained in the firing current after the firing ofthe lamps is utilized to cut off the thyristor 144. For this purpose,the arrangement includes a differentiator 156, 157 whose signal isrectified by a diode 159 and is passed to the control electrode of thethyristor 144 across resistors 160 and 161. For a preferred embodiment,the values of the switching components are as follows:

157 47 ohms 156 100 nF 158 100 kilohms 152 330 F 160 3.3 kilohms 161 4.7kilohms 162 3.3 kilohms In the embodiment according to FIG. 10, atrigger voltage of several thousand volts is developed. A capacitor 168charged to mains voltage level is discharged across a thyristor 165 tothe smaller coil section of the inductance 104, designed as anauto-transformer and having a tap 174. These pulses are stepped up bythe autotransformer and produce the high-voltage pulses desired. Afterfiring, there arises in the smaller winding section an ac. voltage,which is rectified for cut-off of the thyristor 165. Such a firingdevice can also be added as an auxiliary firing in all the othercircuits mentioned in order to increase firing dependability. For apreferred embodiment, the values are:

163 3 3 kilohms 167 3.3 megohms 169 3.3 kilohms 168 16 p.F

170 3.3 kilohms 171 330 .F

172 3 3 kilohms In the embodiment shown in FIG. 11, the firing voltagedeveloped is less high than in the embodiment according to FIG. 10. Theprimary of the inductance 104 acting as an autotransformer receivesabout 1.5 times the mains voltage from a voltage multiplier circuit 182,175, 176 across a switched-on thyristor 180. This value results from thestorage of the voltage developed by the voltage multiplier and stored inthe capacitor 103 in conjunction with superimposition with the nextmains voltage cycle. The autotransformer, formed by the tap 182 on theinductance 104, steps up these voltage peaks by the double to thethreefold mains voltage, for instance. After lamp starting, no furthercharging of the capacitor 103 arises, as the fired lamps no longerpermit any dc voltage charging of the capacitor 103. A preferredembodiment presents the following values:

1 kilohm What is claimed is:

1. A ballast unit for gas discharge lamps having a pair of electrodes,comprising:

a choke means, exclusively for limiting the current to the lamp afterlamp firing, connected in series with the lamp electrodes;

at least one semiconductor switching means, having a control electrode,for brief preheating of the filaments of the lamp at increased ratedcurrent, said switching means being connected in parallel with said lampelectrodes; and

a control circuit means operating in response to an AC voltage suppliedto said lamp electrodes and also connected to said control electrode forinitially triggering said semiconductor means for a predeterminedswitch-on time during each half cycle of said AC voltage, to heat thefilaments of the lamp with an effective current greater than normalrated current, as well as reducing the switch-on time during each halfcycle until the lamp fires, and further increasing voltage peaks acrossthe lamp for a predetermined preheating period prior to reachingignition voltage, thereby avoiding coldstarting of the lamp;

said control circuit means including:

a storage device capable of storing a charge corresponding to thevoltage applied to the lamp;

a discharge resistor connected to said charge storage device; and

overvoltage peak means to cut off any overvoltage peaks.

2. The ballast unit of claim 1 wherein said control circuit connected tosaid semiconductor switching means and said lamp electrodes including alimiting resistor connected to one of said lamp electrodes; a bridgerectifier having an R-C component connected between said limitingresistor and the other of said lamp electrodes; a time element includinga capacitor and a resistor in parallel connected across said bridgerectifier; and control voltage means connected to said bridge rectifierand said limiting resistor including a series resistor, a 'control diodeconnected in series with said re- 9 sistor, and a control capacitorconnecting the junction of said series resistor and said control diodewith said one of said lamp electrodes; and having the following controlstates a. switch-on phase with fully triggeredcontrol-voltage-independent semiconductor switch;

b. starting phase with partly triggered lamp-firingvoltage-dependentsemiconductor switch;

c. protection phase with fault-dependent semiconductor switch;

wherein said control circuit concurrently forms a short circuit forincreased voltages across the gas discharge path so long as the startingphase has not begun, with said limiting resistor forming the loadresistor for said time element and concurrently forming an early firingprotection for the tube, said R-C component of said bridge rectifiertransfering the limiting voltage to the lamp; and, in conjunction withsaid control voltage means, concurrently triggers said semiconductorswitching means.

3. The ballast unit of claim 2 wherein the charging rate of said timeelement and the behavior of said limiting resistor correspond to theheat-up rate of said elec trodes and the cool-down time of saidelectrodes coincides with the discharge time constant of said timeelement for the purpose of skipping part or all of the switch-on andstarting process in the case of a short firing pause.

4. The ballast unit of claim 1 further comprising a capacitor meansconnected in series to said semiconductor switching means for reducingthe apparent resistance of said choke by acting in opposition theretoonly when said semiconductor means is triggered, a trigger diodeconnected to said semiconductor switching means; and voltage dividermeans for fully activating said semiconductor switching means and then,until the beginning of lamp starting, partly activating saidsemiconductor switching means.

5. The ballast unit of claim 1 comprising means for controlling saidsemiconductor switching means in such a manner that a do componentincreased above the shortcircuit current arises for said lamp electrode,

and for preventing early starting of the lamp; wherein said increasedcurrent arises only until the starting of the lamp.

6. The ballast unit of claim 1 including a capacitor connected in serieswith said choke means and in parallel with the lamp, said choke meansbeing tuned substantially to the third harmonic of the mains frequency.

7. The ballast unit of claim 6 comprising a saturation choke connectedin parallel with the gas discharge lamp.

8. The ballast unit of claim 7 comprising a positivetemperature resistorconnected in series with said saturation choke.

9. The ballast unit of claim 7 comprising a thermal cut-out connected inseries with the parallel combination of said lamp and said capacitor.

10. The ballast unit of claim 7 comprising triggering means having apredetermined time constant connected in parallel with the gas dischargelamp and said saturation choke for triggering said semiconductorswitching means and for supplying thereto a cut-off voltage after thestarting of the gas discharge lamp for preventing voltage overload ofsaid semiconductor switching means.

11. The ballast unit of claim 10 comprising d.c. voltage circuit meansfor developing an additional cut-off 10 voltage for preventing voltageoverload of said semiconductor switching means, said dc. voltage circuitmeans having a greater time constant than that of said triggering means.I

12. The ballast unit of claim 6 wherein said choke includes a heaterwinding means for the additional preheating of the electrodes.

13. The ballast unit of claim 12 wherein said control circuit comprisesa resistor, and a capacitive apparent resistance circuit connected inparallel with said resistor; wherein said semiconductor switching meansis a triac.

14. The ballast unit of claim 12 comprising a capacitor connected inparallel with said semiconductor switching means, said semiconductorswitching means having a control electrode, for cold-startingprotection, a diode and a resistor bridging said semiconductor switchingmeans, and a cut-off circuit and a safety cutoff circuit both connectedto said control electrode of said semiconductor switching means.

15. The ballast unit of claim 12 comprising a differentiator andrectifier means connected to said semiconductor switching means forcutting off said semiconductor switching means.

16. A ballast unit according to claim 1, wherein: said storage devicecompensates at least in part for the resistance of said choke means,

said storage device operating exclusively in said control circuit duringthe heating of said filaments of the lamp and being inoperative afterthe lamp fires.

17. A ballast unit according to claim 1, wherein the apparent resistanceof said storage device is approximately 2 3 times smaller than saidballast choke means.

18. A ballast unit according to claim 1, wherein said control circuitmeans further includes a heater circuit;

said heater circuit being asymmetrically loaded only until the lampfires;

said heater circuit including a diode and a VDR connected in parallel,the parallel combination being connected in series with one of the pairof lamp electrodes and with said at least one semiconductor switchingmeans; and

a damping resistor and damping capacitor connected in series with eachother and said VDR, and in parallel with said semiconductor switchingmeans, whereby an increased direct current component in excess of shortcircuit current is produced in said heater circuit.

19. A ballast unit according to claim 1, wherein said control circuitmeans further includes a heating circuit; said heating circuit beingasymmetrically loaded only until the lamp fires;

a storage capacitor connected through a storage capacitor resistor tosaid control electrode and being chargeable by the lamp voltage;

a further resistor connecting one of said pair of lamp electrodes tosaid control electrode;

a charging current diode electrically connected to one of said pair oflamp electrodes and to said storage capacitor;

said heating circuit being connected to the lamp such that the cut-offvoltage component of said storage capacitor counteracts the cut-offvoltage component of the lamp voltage, and the time constant of saidstorage capacitor being such that the filament of the lamp reaches aglowing state prior to the charge on said storage capacitor reachingmaxiand said primary firing circuit.

21. The ballast unit of claim 20, further comprising a primary firingcircuit connected to said primary auxiliary winding having capacitormeans for providing the triggering energy, converting the ballast unitinto a wattless-current-compensated ballast unit, providing anovervoltage peak protection for said semiconductor switching means anddeveloping the lamp firing voltage in said secondary auxiliary winding;wherein said semiconductor switching means closes said heating circuit

1. A ballast unit for gas discharge lamps having a pair of electrodes, comprising: a choke means, exclusively for limiting the current to the lamp after lamp firing, connected in series with the lamp electrodes; at least one semiconductor switching means, having a control electrode, for brief preheating of the filaments of the lamp at increased rated current, said switching means being connected in parallel with said lamp electrodes; and a control circuit means operating in response to an AC voltage supplied to said lamp electrodes and also connected to said control electrode for initially triggering said semiconductor means for a predetermined switch-on time during each half cycle of said AC voltage, to heat the filaments of the lamp with an effective current greater than normal rated current, as well as reducing the switch-on time during each half cycle until the lamp fires, and further increasing voltage peaks across the lamp for a predetermined preheating period prior to reaching ignition voltage, thereby avoiding cold-starting of the lamp; said control circuit means including: a storage device capable of storing a charge corresponding to the voltage applied to the lamp; a discharge resistor connected to said charge storage device; and overvoltage peak means to cut off any overvoltage peaks.
 2. The ballast unit of claim 1 wherein said control circuit connected to said semiconduCtor switching means and said lamp electrodes including a limiting resistor connected to one of said lamp electrodes; a bridge rectifier having an R-C component connected between said limiting resistor and the other of said lamp electrodes; a time element including a capacitor and a resistor in parallel connected across said bridge rectifier; and control voltage means connected to said bridge rectifier and said limiting resistor including a series resistor, a control diode connected in series with said resistor, and a control capacitor connecting the junction of said series resistor and said control diode with said one of said lamp electrodes; and having the following control states a. switch-on phase with fully triggered control-voltage-independent semiconductor switch; b. starting phase with partly triggered lamp-firing-voltage-dependent semiconductor switch; c. protection phase with fault-dependent semiconductor switch; wherein said control circuit concurrently forms a short circuit for increased voltages across the gas discharge path so long as the starting phase has not begun, with said limiting resistor forming the load resistor for said time element and concurrently forming an early firing protection for the tube, said R-C component of said bridge rectifier transfering the limiting voltage to the lamp; and, in conjunction with said control voltage means, concurrently triggers said semiconductor switching means.
 3. The ballast unit of claim 2 wherein the charging rate of said time element and the behavior of said limiting resistor correspond to the heat-up rate of said electrodes and the cool-down time of said electrodes coincides with the discharge time constant of said time element for the purpose of skipping part or all of the switch-on and starting process in the case of a short firing pause.
 4. The ballast unit of claim 1 further comprising a capacitor means connected in series to said semiconductor switching means for reducing the apparent resistance of said choke by acting in opposition thereto only when said semiconductor means is triggered, a trigger diode connected to said semiconductor switching means; and voltage divider means for fully activating said semiconductor switching means and then, until the beginning of lamp starting, partly activating said semiconductor switching means.
 5. The ballast unit of claim 1 comprising means for controlling said semiconductor switching means in such a manner that a d.c. component increased above the shortcircuit current arises for said lamp electrode, and for preventing early starting of the lamp; wherein said increased current arises only until the starting of the lamp.
 6. The ballast unit of claim 1 including a capacitor connected in series with said choke means and in parallel with the lamp, said choke means being tuned substantially to the third harmonic of the mains frequency.
 7. The ballast unit of claim 6 comprising a saturation choke connected in parallel with the gas discharge lamp.
 8. The ballast unit of claim 7 comprising a positive-temperature resistor connected in series with said saturation choke.
 9. The ballast unit of claim 7 comprising a thermal cut-out connected in series with the parallel combination of said lamp and said capacitor.
 10. The ballast unit of claim 7 comprising triggering means having a predetermined time constant connected in parallel with the gas discharge lamp and said saturation choke for triggering said semiconductor switching means and for supplying thereto a cut-off voltage after the starting of the gas discharge lamp for preventing voltage overload of said semiconductor switching means.
 11. The ballast unit of claim 10 comprising d.c. voltage circuit means for developing an additional cut-off voltage for preventing voltage overload of said semiconductor switching means, said d.c. voltage circuit means having a greater time constant than that of said triggering means.
 12. The ballast unit of claim 6 wherein said choke includes a heater winding means for the additional preheating of the electrodes.
 13. The ballast unit of claim 12 wherein said control circuit comprises a resistor, and a capacitive apparent resistance circuit connected in parallel with said resistor; wherein said semiconductor switching means is a triac.
 14. The ballast unit of claim 12 comprising a capacitor connected in parallel with said semiconductor switching means, said semiconductor switching means having a control electrode, for cold-starting protection, a diode and a resistor bridging said semiconductor switching means, and a cut-off circuit and a safety cut-off circuit both connected to said control electrode of said semiconductor switching means.
 15. The ballast unit of claim 12 comprising a differentiator and rectifier means connected to said semiconductor switching means for cutting off said semiconductor switching means.
 16. A ballast unit according to claim 1, wherein: said storage device compensates at least in part for the resistance of said choke means, said storage device operating exclusively in said control circuit during the heating of said filaments of the lamp and being inoperative after the lamp fires.
 17. A ballast unit according to claim 1, wherein the apparent resistance of said storage device is approximately 2 - 3 times smaller than said ballast choke means.
 18. A ballast unit according to claim 1, wherein said control circuit means further includes a heater circuit; said heater circuit being asymmetrically loaded only until the lamp fires; said heater circuit including a diode and a VDR connected in parallel, the parallel combination being connected in series with one of the pair of lamp electrodes and with said at least one semiconductor switching means; and a damping resistor and damping capacitor connected in series with each other and said VDR, and in parallel with said semiconductor switching means, whereby an increased direct current component in excess of short circuit current is produced in said heater circuit.
 19. A ballast unit according to claim 1, wherein said control circuit means further includes a heating circuit; said heating circuit being asymmetrically loaded only until the lamp fires; a storage capacitor connected through a storage capacitor resistor to said control electrode and being chargeable by the lamp voltage; a further resistor connecting one of said pair of lamp electrodes to said control electrode; a charging current diode electrically connected to one of said pair of lamp electrodes and to said storage capacitor; said heating circuit being connected to the lamp such that the cut-off voltage component of said storage capacitor counteracts the cut-off voltage component of the lamp voltage, and the time constant of said storage capacitor being such that the filament of the lamp reaches a glowing state prior to the charge on said storage capacitor reaching maximum value.
 20. The ballast unit according to claim 1 further comprising an auxiliary winding including a primary and secondary winding serially interconnected in the parallel path of said semiconductor means and said lamp electrodes, said choke means and said auxiliary winding being wound to a same iron core in opposite winding directions, said auxiliary winding having the same number of windings as said choke means.
 21. The ballast unit of claim 20, further comprising a primary firing circuit connected to said primary auxiliary winding having capacitor means for providing the triggering energy, converting the ballast unit into a wattless-current-compensated ballast unit, providing an overvoltage peak protection for said semiconductor switching means and developing the lamp firing voltage in said secondary auxiliary winding; wherein said semiconductor switching means closes said heating circuit and said primary firing circuit. 